Ceph: monitor store taking up a lot of space

During some strange circonstances, the levelDB monitor store can start taking up a substancial amount of space. Let quickly see how we can workaround that.

The result is basically overgrown SSTS file from levelDB. SST stands for Sorted String Table, which means that these files are responsable for indexing and storing key/value sets. The only known workaround at this point in time is to add the following in your [mon] section from your ceph.conf:

mon compact on start = true

Then restart your ceph-mon process, this will result in a major cleanup of these SST files.

Another quick tip to debug levelDB issue is to activate this option to get a full debug log:

osd leveldb paranoid = true
osd leveldb log = /var/log/ceph/osd/ceph-osd.1.log.leveldb

You can also compat it on the fly:

$ sudo ceph tell mon.{id} compact